Abstract
A model for simulation of wheat root growth under non-optimal conditions has been developed. The following influences on root growth are considered: soil temperature; soil water suction and mechanical resistance dependent on soil density and soil water content; the occurrence of soil cracks. The probability of root tips finding cracks, where unimpeded growth can occur, is given special consideration, including the effect of changes in the crack system with changes in soil water content. Water uptake is calculated, and by use of a transpiration coefficient an estimate of dry-matter production is made. This is partitioned between roots, leaves and stem and later grain. Effects of soil fertility are not yet considered in this model. A sensitivity analysis of the model was made by varying the soil density profile, the occurrence of cracks, sowing date and plant density for several years of weather data. The variability, caused by the fact that only a limited number of root axes was simulated in each run and guided by random numbers, was also investigated. The model can be used to assess the effects of compaction on wheat yield, and also the likely benefits which may be derived from sub-soiling or slit-tillage. The model is written in Digital's VAX FORTRAN language, and a run for one growing season takes less than 10 seconds of CPU-time on a VAX 11/785 computer.
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